From 71d2cfb652e92d624f9e3a7e7df5246a92ff621c Mon Sep 17 00:00:00 2001
From: Torsten Harenberg <harenberg@physik.uni-wuppertal.de>
Date: Mon, 3 Feb 2025 15:37:45 +0100
Subject: [PATCH] Avoid calling GetModemStatusBits on Android. Should fix #1

---
 cts.go         | 14 ++++++++++++++
 cts_android.go |  9 +++++++++
 ptc.go         | 31 ++++++++++++++-----------------
 3 files changed, 37 insertions(+), 17 deletions(-)
 create mode 100644 cts.go
 create mode 100644 cts_android.go

diff --git a/cts.go b/cts.go
new file mode 100644
index 0000000..c25cb69
--- /dev/null
+++ b/cts.go
@@ -0,0 +1,14 @@
+//go:build !android
+
+package main
+
+import "github.com/albenik/go-serial/v2"
+
+// cts returns the clear-to-send status of a device. On Android it will return true as GetModemStatusBits() fails there.
+func cts(p *serial.Port) (bool, error) {
+	r, err := p.GetModemStatusBits()
+	if err != nil {
+		return false, err
+	}
+	return r.CTS, nil
+}
diff --git a/cts_android.go b/cts_android.go
new file mode 100644
index 0000000..cfddd38
--- /dev/null
+++ b/cts_android.go
@@ -0,0 +1,9 @@
+//go:build android
+
+package main
+
+import "github.com/albenik/go-serial/v2"
+
+func cts(_ *serial.Port) (bool, error) {
+	return true, nil
+}
diff --git a/ptc.go b/ptc.go
index 1ca139e..7d25b9c 100644
--- a/ptc.go
+++ b/ptc.go
@@ -761,12 +761,15 @@ func (p *Modem) _write(cmd string) error {
 	defer p.mux.device.Unlock()
 	out := cmd + "\r"
 	for {
-		status, err := p.device.GetModemStatusBits()
+
+		// check if the serial line is clear-to-send
+		status, err := cts(p.device)
 		if err != nil {
 			writeDebug("GetModemStatusBits failed. cmd: "+cmd+" Error: "+err.Error(), 1)
 			return err
 		}
-		if status.CTS {
+
+		if status {
 			for {
 				sent, err := p.device.Write([]byte(out))
 				if err == nil {
@@ -788,13 +791,13 @@ func (p *Modem) _write(cmd string) error {
 // Although these functions are small, I prefer to keep their functionality
 // separate. They follow the steps in the SCS documentation
 
-// helper function: de-hexlify and write to debug channel
+// printhex: helper function: de-hexlify and write to debug channel
 func printhex(s string) {
 	t, _ := hex.DecodeString(s)
 	writeDebug(string(t), 3)
 }
 
-// helper function: "unstuff" a string
+// unstuff: helper function: "unstuff" a string
 func unstuff(s string) string {
 	//Expect: the string contains aa aa at the beginning, that should NOT be
 	//stuffed
@@ -806,7 +809,7 @@ func unstuff(s string) string {
 	return re
 }
 
-// helper function: "stuff" a string: replaces every #170 with #170#0
+// stuff: helper function: "stuff" a string: replaces every #170 with #170#0
 func stuff(s string) string {
 	//Expect: the string contains aa aa at the beginning, that should NOT be
 	//stuffed
@@ -822,14 +825,14 @@ func stuff(s string) string {
 	return re
 }
 
-// helper function: calculates the CCITT-CRC16 checksum
+// checksum: helper function: calculates the CCITT-CRC16 checksum
 func checksum(s string) uint16 {
 	tochecksum, _ := hex.DecodeString(s[4:])
 	chksum := bits.ReverseBytes16(crc16.ChecksumCCITT([]byte(tochecksum)))
 	return chksum
 }
 
-// helper fuction: check the checksum by comparing
+// checkcrc: helper fuction: check the checksum by comparing
 func checkcrc(s []byte) bool {
 	tochecksum := s[2 : len(s)-2]
 	chksum := bits.ReverseBytes16(crc16.ChecksumCCITT(tochecksum))
@@ -837,7 +840,7 @@ func checkcrc(s []byte) bool {
 	return (binary.BigEndian.Uint16(pksum) == chksum)
 }
 
-// super helper fuction: convert an ordinary WA8DED message into a CRC-Hostmode message
+// docrc: super helper fuction: convert an ordinary WA8DED message into a CRC-Hostmode message
 func docrc(msg string) string {
 	// step 1: add a #170170
 	msg = fmt.Sprintf("%02x%02x%s", 170, 170, msg)
@@ -850,9 +853,7 @@ func docrc(msg string) string {
 
 }
 
-// Write channel to serial connection (NOT thread safe)
-//
-// If used, make shure to lock/unlock p.mux.pactor mutex!
+// writeChannel: Write channel to serial connection (NOT thread safe)- If used, make sure to mutex!
 func (p *Modem) writeChannel(msg string, ch int, isCommand bool) error {
 	if err := p.checkSerialDevice(); err != nil {
 		writeDebug(err.Error(), 1)
@@ -905,18 +906,14 @@ func (p *Modem) writeChannel(msg string, ch int, isCommand bool) error {
 	return nil
 }
 
-// Read from serial connection (thread safe)
-//
-// No other read/write operation allowed during this time
+// read: Read from serial connection (thread safe)
 func (p *Modem) read(chunkSize int) (int, []byte, error) {
 	p.mux.pactor.Lock()
 	defer p.mux.pactor.Unlock()
 	return p._read(chunkSize)
 }
 
-// Read from serial connection (NOT thread safe)
-//
-// If used, make shure to lock/unlock p.mux.pactor mutex!
+// _read: Read from serial connection (NOT thread safe). To be used from read
 func (p *Modem) _read(chunkSize int) (int, []byte, error) {
 	if err := p.checkSerialDevice(); err != nil {
 		writeDebug(err.Error(), 1)